Datasheet

326
XMEGA B [DATASHEET]
8291B–AVR–01/2013
Figure 26-1. ADC overview.
26.3 Input Sources
Input sources are the voltage inputs that the ADC can measure and convert. Four types of measurements can be
selected:
 Differential input
 Differential input with gain
 Single-ended input
 Internal input
The input pins are used for single-ended and differential input, while the internal inputs are directly available inside the
device. In devices with two ADCs, PORTA pins can be input to ADCA and PORTB pins can be input to ADCB. For the
devices with only one ADC, input pins may be available for ADCA on both PORTA and PORTB.
The ADC is differential, and so for single-ended measurements the negative input is connected to a fixed internal value.
The four types of measurements and their corresponding input options are shown in Figure 26-2 on page 327 to Figure
26-6 on page 329.
26.3.1 Differential Input
When differential input is enabled, all input pins can be selected as positive input, and input pins 0 to 3 can be selected
as negative input. The ADC must be in signed mode when differential input is used.
CH0 Result
Compare
Register
<
>
Threshol
d
(Int Req
)
Internal 1.00V
Internal VCC/1.6V
AREFA
AREFB
V
INP
V
INN
Internal
signals
S&H Σ
ADC
DAC
2x
2 bits
V
IN
V
OUT
Internal VCC/2
ADC0
A
DC15
•
•
•
ADC0
ADC7
•
•
•
Reference
Voltage
Stage
1
Stage
2
Digital Correction Logic
2
2
clk
ADC
CH0.CTRL REFCTRL
CH0.MUXCTRL
EVCTRLCTRLA
CTRLB
Enable
Start
Mode
Resolution
Action
Select